Skip to content

A Guide to ANSI Flanges and its Dimensions

ANSI flanges are integral components in the PVF world. They connect the pipes, valves, and various other fittings within a pipeline or assembly. Industries like chemical processing, food processing, and petrochemical processing, cannot do much without these flanges.

If you’re from any of these industries and are keen to know more about ANSI flanges, their dimensions, and their types, this guide is exactly what you need.

What are ANSI Flanges?

Established in 1918, the American National Standards Institute supervises national standards and accreditation systems for services, processes, etc., in the United States. To ensure the international influence and relevance of ANSI standards, ANSI works with U.S. government agencies, organizations, and international entities.

Before ANSI, member organizations of the United Engineering Societies were developing engineering and equipment standards. These Societies include the American Society of Mechanical Engineers, the American Institute of Electrical Engineers, Metallurgical and Petroleum Engineers (AIME), the American Institute of Mining, the American Society of Civil Engineers (ASCE), and ASTM International.

ANSI is a private and non-profit organization that aims to develop stringent standards for numerous sectors, including industrial flanges as developed by ASME.

These standards specify flanges’ dimensions, size, design, and even material grade. Compliance with standards ensures reliability, safety, and efficiency. Additionally,

ANSI flanges easily integrate with components from other manufacturers. Therefore, many industries choose ANSI flanges over other less stringent existing specifications. 

What is the role of ANSI Flanges in Different Industries?

ANSI flanges play an essential role in the following industries:

Oil, Gas, and Chemical Industry

Oil, Gas, and Chemical Industries depend on flanges to provide safe and effective operations within complex assemblies. Flanges connect pipes and equipment in the several stages of oil and gas extraction, transportation, and refining.

In chemical facilities, flanges connect pipelines carrying dangerous or corrosive chemicals, allowing secure and effective movement of fluid and gases during operation.

Food Processing and Manufacturing

Food Processing and Manufacturing industries use ANSI flanges more frequently than simply AWWA or API specifications. Standard applications include joining pipes in beverage processing, dairy production, and bakery operations.

In both sectors, flanges are known for efficient operations and adherence to quality standards, making them integral components.

Waterworks and Municipal Pipe Systems

ANSI and AWWA flanges enable robust joints for seamlessly transporting and distributing water and other fluids. Flanges attach pipes carting treated water to storage tanks and dispersal networks in water treatment plants.

In municipal pipe systems, flanges connect different-sized pipes, enabling water supply to various locations within a zoned and often highly populated area.

Valves, Vessels, and Industrial Pumps

Flanges are crucial for establishing dependable and secure connections in the valves, vessels, and industrial pumps industries. Flanges join the pipes in valves to control fluid flow, making them essential to distribute water, gas, and oil pipelines.

Flanges link pipes to vessels, such as tanks and reactors, for filling, emptying, and monitoring activities in sectors like chemical manufacturing. To connect the intake and exit pipes of industrial pumps, known as flanges, efficiently transfer liquids in industries including mining and wastewater treatment.

Heating Systems and Heat Exchangers

Flanges aid in the effective transfer and control of thermal energy. Their operation ensures dependable distribution of hot water or steam to radiators or other heat emitters. Flanges join fluid-carrying tubes in heat exchangers, which are crucial in HVAC and power production and enable heat transfer between various media.

Plumbing and Mechanical Systems

Flanges attach pipes in water supply and drainage systems, stopping leaks and guaranteeing steady fluid flow. Additionally, they link showers, sinks, and other fixtures to the plumbing system. Pumps, motors, and valves are connected by flanges in mechanical systems, making maintenance and repairs simple.

Power Plants and the Nuclear Power Industry

Power plants and the nuclear power sector rely heavily on flanges to maintain their systems’ safety, effectiveness, and functionality. They join pipes in steam and water circuits, aiding the movement of steam and heat while producing electricity.

They are essential for joining pipes transporting coolant in nuclear reactors to control temperature and avert mishaps.

What are ANSI Flange Sizes?

ANSI flanges are available in various sizes. Here is the list.



ANSI Flanges - Class 400

ANSI Flanges-class 600

ANSI Flanges - Class 900

ANSI flanges - Class 1500

ANSI Flanges -class 2500

Above All Images Credits:-

Which Factors Influencing ANSI Flange Size?

Choosing the right ANSI flange size can be tricky, but basic context from your application can help you make an informed decision. The foremost question regarding flange selection is ANSI flange size.

The accurate flange size ensures safe and smoother operation for your body of work, as the scale of your project cannot be realized without its proper selection.

Pipe Diameter Impact

The diameter of the pipe influences the flange size. As we just mentioned, it is one of the essential factors that we should consider. The flange size should match the pipe’s outer diameter to ensure a proper fit and seal.

It helps to prevent leakage, as there is no desire for structural issues in your piping system. Therefore, gauge the pipe diameter to choose the appropriate flange size.

Pressure and Temperature Considerations

Selecting an ANSI flange size requires careful consideration of pressure and temperature. Various flange types can withstand various pressure and temperature levels.

If your pipe system operates at extreme pressures or temperatures, you’ll require a wider, more robust flange to endure these circumstances safely. Smaller flanges would work well if your industrial application operates on low pressure and pressure.

It would cut costs and complexity. As a rule of thumb, the higher the pressure class, the larger the overall thickness measurements of the flange.

Importance of Industry Standards

Flanges must adhere to ANSI flange standards. These standards provide guidelines for flange sizes, dimensions, and materials. It ensures compatibility and safety in your piping system.

By selecting an ANSI-compliant flange, you can be sure it will integrate flawlessly with other ANSI-compliant parts, lowering the possibility of leaks and malfunctions. Additionally, various industries prioritize safety and regulatory compliance to adhere to these standards.

What are ANSI Flange Dimensions?

The ANSI flanges key dimensions include inner and outer diameter and bolt-hole spacing. Let’s explore these dimensions and why they are crucial:

 Inner Diameter (I.D.):

1. It is a measurement of the bore or opening in the center of the flange.

2. The inner diameter defines the piping system’s flow capacity, and the flange’s inner diameter must match the connected pipes.

3. Adequate alignment of the inner diameters with the connecting pipe prevents turbulence and pressure drops, ensuring efficient fluid flow.

Outer Diameter (O.D.):

1. It is the measurement of the outside edge of the flange.

2. It helps determine the flange size and the required gasket size.

3. The outer diameter should be compatible with the dimensions of the adjacent components to ensure a secure and leak-free connection.

Bolt-Hole Spacing:

1. It is the distance between the bolt holes set in a circular pattern on the flange.

2. The number of bolt holes and their spacing depend on the flange size and pressure rating.

3. Proper bolt-hole spacing is essential for uniform distribution of the bolt load, ensuring a tight seal and preventing leakage.

4. The spacing should also match the mating flange for a secure connection.

These dimensions are crucial for several reasons:

1. Interchangeability: With an ANSI-compliant flange, you can be sure it will integrate with other components effortlessly. It lowers the possibility of leaks and malfunctions. 

2. Safety: Proper dimensions prevent pressure-related failure of the flange. It is essential for both the system’s and the user’s safety.

3. Leak Prevention: Precise specifications, inner and outer diameters, and bolt-hole spacing are essential for a tight seal. It stops leakage that can cause product loss, environmental harm, or safety risks.

4. Efficiency: The matched inner diameter of the flange with the pipe’s inner diameter reduces turbulence and pressure drops, optimizing the efficiency of the fluid handling system.

5. Consistency: Standardized dimensions make replacing or upgrading components within a pipe system easier by promoting consistency in design and production.

Accessing ANSI Flange Dimensions

ANSI B16.5 Standard

ASME B16.5 standard includes Steel Pipe Flanges and changed fittings from NPS 1/2 to NPS 24 Metric/Inch in Pressure Classes 150 to 2500. It covers materials, dimensions, tolerances, marking, pressure-temperature ratings, testing, and processes of designating openings for pipe flanges and flanged fittings.

Weld neck and blind flanges are two crucial flanges frequently used in pipe systems. “B16.5” and “B16 5” are interchangeable and refer to the same standard. However, keep in mind that the ASME B16 5 (ANSI B16 5) standard only addresses sizes up to 24 inches, as sizes larger than this begin to deviate to B16.1 and B16.47.

Role of ANSI in standardizing flange dimensions

Imagine if you would that there are no stringent standards in the PVF world, and components aren’t designed to fit together like they should. What would happen in this situation? It would lead to leakage, pipe bursts, and untold operational hazards. Fortunately, this is not the case.

To address this challenge in its totality, ANSI B16.5 covers all necessary issues regarding flange design and material selection. Let’s explore its role in standardizing flange dimensions.


Flanges are the unsung heroes that connect everything in the complex world of pipes, valves, and industrial machinery. Different manufacturers may build flanges with very modest size variances and alterations in assumed base thickness. For those applications requiring a tried and true industry application,  ANSI B16.5 steps in, donning its cape of standardization

Safety First

Industries prioritize safety. Placing a square peg into a circular hole is impossible when flanges are improperly aligned. There may be leaks, pressure discrepancies, or even catastrophic breakdowns. Risks simply do not need to be taken when good standards exist.

Flanges must adhere to strict specifications, which are ensured by ANSI B16.5, preventing accidents and ensuring everyone’s safety.

Easier Life

Industries can use flanges from various manufacturers interchangeably without fear, saving them both time and money—less downtime results from smoother maintenance and repairs.

ANSI 300 Flange Dimensions

In many industrial piping systems, ANSI 300 flanges are commonly used. While slightly less popular than class 150, we would like to highlight their purpose for the sake of their compatibility with orifice unions.

What makes them unique? Well, it’s their pressure handling capacity that we call pressure rating. Their design can handle high-pressure environments and become the top choice for many industries where high pressure is a concern. 

Pressure Rating

The “300” in ANSI 300 flanges refers to its pressure class, which is nominally 300. However, it is important to remember that class is not interchangeable with operating pressure. Look at the values for pressure-temperature data within the B16.5 specification.

For B16.36, have a look at the orifice unions which start at this 300-pound pressure class. This is all critical information because it demonstrates the strength with which these flanges can resist heavy pressure without yielding to operational failure, especially when instrumentation is utilized.

Applications in High-Pressure Systems

The pressure inside the pipes is extreme in sectors like oil and gas, chemical processing, and power generation; ANSI 300 and higher class flanges are applicable here, with higher pressure classes allowing for more extreme scenarios.

ANSI flanges are a staple for connecting pipelines in offshore rigs and onshore facilities in the oil and gas industry. They ensure that oil and gas can be transported safely, even under extreme pressure conditions.

Chemical plants deal with corrosive and high-pressure substances. ANSI flanges are preferable for connecting pipes in these environments, ensuring the chemicals flow smoothly without any leaks or mishaps. Material grade selection is crucial to prevent corrosion.

Power plants require piping systems to handle the intense pressure generated during energy production. ANSI 300 and higher pressure class flanges play a vital role in maintaining the integrity of these systems.

ANSI flanges aid in maintaining the effectiveness of high-pressure systems in steel manufacture and production. Their selection ensures that production installation and operational procedures go off without a hitch.

ANSI 150 Flange

The most basic and popular of all classes – ANSI 150 flanges meet specific standards of the American National Standards Institute. Here, the number ‘150’ refers to the flange’s pressure class, though the operational pressure rating is normally higher. The B16.5 spec indicates that these flanges can handle moderate pressure with ease.

Characteristics of ANSI 150 Flanges

Do you know what makes ANSI 150 flanges special? Let’s take a look at their key characteristics:

Versatility: ANSI 150 flanges are versatile. They can join pipes made of many materials, including copper, steel, and plastic. They are ideal for a wide range of applications due to their versatility.

Ease of Installation: These flanges are easy to install. Their bolt-hole pattern and standardized dimensions make installation effortless and put them in place efficiently.

Durable: ANSI 150 flanges are durable. They have a long service life because they can withstand severe weather and are composed of corrosion-resistant materials like stainless steel.

Leak-Resistant: Their flat-face design, coupled with gaskets, ensures a tight, leak-resistant seal when connecting pipes or other equipment.

Why ANSI 150 Flanges Are Popular

So, what’s the secret behind the popularity of ANSI 150 flanges?

Cost-Effective: ANSI 150 flanges are an appealing option for projects on a tight budget because they provide a trustworthy solution without breaking the bank.

Widespread Availability: Flanges come in various sizes and materials, so choosing the correct flange for your needs is simple.

Broad Application Range: Plumbing, HVAC, chemical processing, and water treatment plants are just a few of the industries that use ANSI 150 flanges. They are appropriate for various applications due to their versatility and mild pressure rating.

Proven Reliability: ANSI 150 flanges have demonstrated their dependability in countless installations. Engineers and experts rely on them to build reliable and secure connections.


ANSI flanges are the backbone of many systems. They are essential for ensuring fluid movement through pipes and equipment safely and smoothly due to their standardized dimensions, precision engineering, and dependability. So, the next time you see a flange in use, you’ll know it’s silently carrying out its function and keeping the piping industry in operation.


Q.1 What’s the significance of the Outside Diameter (O.D.) in ANSI flanges?

The O.D. is the outer measurement of the flange. Knowing the O.D. helps determine whether the flange is compatible with the pipe or equipment it’s meant to connect.

Q.2 What are the key dimensions to consider when working with ANSI flanges?

The critical dimensions for ANSI flanges include Nominal Pipe Size (NPS), Outside Diameter (O.D.), Inside Diameter (I.D.), flange face type (raised face or flat face), bolt hole diameter and bolt circle, flange thickness, and the number of bolt holes.

Q.3 What role does the number of bolt holes play in ANSI flanges?

The number of bolt holes evenly distributes the load across the flange, ensuring a secure and stable connection between the flange and the adjoining equipment or pipe.

Q.4 Do ANSI flanges come in different pressure ratings, and how do I choose the right one?

Yes, ANSI flanges come in different pressure ratings, ranging from 75  to 2500 PSI. Choosing the right pressure rating depends on the specific requirements of your piping system and the pressure it needs to handle.

0 0 votes
Article Rating
Notify of
Newest Most Voted
Inline Feedbacks
View all comments
7 months ago

The comprehensive role of ANSI flanges across various industries, from oil and gas to food processing, truly underscores their indispensability in ensuring safe and efficient operations within complex assemblies.

7 months ago

It’s fascinating to see how ANSI flanges, through their standardized dimensions and material specifications, significantly contribute to safety and reliability in numerous sectors like power plants, plumbing systems, and even the nuclear power industry.

7 months ago

Do ANSI flanges come in different pressure ratings, and how do I choose the right one?

7 months ago
Reply to  Peter

Yes, ANSI flanges come in different pressure ratings, ranging from 75 to 2500 PSI. Choosing the right pressure rating depends on the specific requirements of your piping system and the pressure it needs to handle.

7 months ago

What are the key dimensions to consider when working with ANSI flanges? 

7 months ago
Reply to  Jimmy

The critical dimensions for ANSI flanges include Nominal Pipe Size (NPS), Outside Diameter (O.D.), Inside Diameter (I.D.), flange face type (raised face or flat face), bolt hole diameter and bolt circle, flange thickness, and the number of bolt holes.

7 months ago

The way ANSI B16.5 standardizes flange dimensions and bolsters compatibility between various manufacturers’ components exemplifies how standardized protocols mitigate operational hazards and ensure smoother operations.

Jeff B.
Jeff B.
6 months ago

Another good article. You guys are killing it.

4 months ago

I wholeheartedly endorse every idea you’ve outlined in your post. They are undeniably persuasive and will undoubtedly be successful. However, the postings are rather brief for novice readers; could you kindly extend them slightly in the future? I appreciate the post.